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ListBox.Items.Add is slow and flickers


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Adding a (larger) group of entries to a ListBox is very slow,
because after every "items.add" call the ListBox is repainted.

There are two ways to overcome this:

  • use the Windows message WM_SETREDRAW (see Win32.hlp for details).
    The VCL provides two methods for this: BeginUpdate and EndUpdate.
    I would assume that this is faster than method #2.
  • read the strings in a temporary TStringList object.
    Maybe you already have such a list - in this case you should use your existing list.
    Then use the Assign method to transfer the whole list.
Some sample code after a contribution from Bjrn:

// method #1
procedure TForm1.Button1Click(Sender: TObject);
  i : integer;
  for i:=1 to maxitems do

// method #2
procedure TForm1.Button2Click(Sender: TObject);
  i  : integer;
  tmp: tstringlist;
  for i:=1 to maxitems do

Content-type: text/html


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